Abstract

Kaposi’s sarcoma–associated herpesvirus (KSHV) is a gammaherpesvirus that is the etiological agent of the endothelial cell cancer Kaposi’s sarcoma (KS) and 2 B cell lymphoproliferative disorders, primary effusion lymphoma (PEL) and multicentric Castleman’s disease (MCD). KSHV ORF36, also known as viral protein kinase (vPK), is a viral serine/threonine kinase. We previously reported that KSHV vPK enhances cell proliferation and mimics cellular S6 kinase to phosphorylate ribosomal protein S6, a protein involved in protein synthesis. We created a mouse model to analyze the function of vPK in vivo. We believe this is the first mouse tumor model of a viral kinase encoded by a pathogenic human virus. We observed increased B cell activation in the vPK transgenic mice compared with normal mice. We also found that, over time, vPK transgenic mice developed a B cell hyperproliferative disorder and/or a high-grade B cell non-Hodgkin lymphoma at a greatly increased incidence compared with littermate controls. This mouse model shows that a viral protein kinase is capable of promoting B cell activation and proliferation as well as augmenting lymphomagenesis in vivo and may therefore contribute to the development of viral cancers.

Figure 1

FLAG-tagged vPK was cloned, using HinDIII-HF and BamHI-HF, into a plasmid containing a Ub- and hGH-stabilization element. The linearized transgene fragment was microinjected into the embryos of C57BL/6 mice and implanted into pseudopregnant female mice. Each vPK line was developed from breeding a vPK founder to a C57BL/6 mouse. (A) Schematic of the linearized construct used to generate the vPK transgenic mice, as well as the cut sites and probe for the Southern blot in D. (B) DNA from the tails of 2 WT (wA and wB) and 2 vPK transgenic mice (vA and vB) for lines 1 and 2 was isolated and evaluated by PCR for the vPK transgene. (C) Expression of vPK protein in lysates from spleens of the mice in B as determined by SDS-PAGE and Western blot. Lysate from HEK-293 cells that transiently express vPK was used as a positive control for vPK expression. (D) Southern blot of WT, vPK1, and vPK2. DNA was isolated from the spleens of WT and vPK lines 1 and 2. D, double digest with HinDIII-HF and BamHI-HF; S, single digestion with AFlII; p-vPK, plasmid Ub.vPK.hGH.